1. Field of the Invention
For layer formation, diffusion, baking and the like of a semiconductor wafer (hereinafter called a xe2x80x9cwaferxe2x80x9d), a heat treatment device of the light irradiation type is used, in which the article to be treated is rapidly heated, held at a high temperature, and quickly cooled. As a light source for this purpose, a filament lamp is used. Furthermore, for semiconductor lithography, for curing, drying of ink and adhesive, and for similar purposes a discharge lamp, such as a super-high pressure mercury lamp, high pressure mercury lamp, or the like is used. The present invention relates to a process for determination of blackening of a lamp in which the blackening of a lamp, such as the above described filament lamp, discharge lamp, and the like can be determined without visual inspection.
2. Description of Related Art
Heat treatment of the light irradiation type in the production of semiconductors is performed in broad areas, such as layer formation, diffusion, baking and the like.
In each of these treatments, a wafer is heated to a high temperature. If a heat treatment device of the light irradiation type is used for the heat treatment, the wafer can be quickly heated. The temperature of the wafer can be increased to at least 1000xc2x0 C. in a time frame of between a few seconds and a few dozen seconds. Furthermore, rapid cooling can be achieved when the light irradiation stops.
FIG. 10 is a schematic representation of an example of the above described heat treatment device of the light irradiation type. In the figure, a heat treatment device 10 of the light irradiation type comprises several filament lamps 1 for heat treatment and mirrors 2. To subject a workpiece W to heat treatment, the workpiece W, for example, a wafer or the like, is placed on a holder 3 of ceramic or the like, and then, in a treatment chamber in which the above described filament lamps 1 and mirrors 2 are located. By operating the filament lamps 1, the article to be treated is irradiated with the light emitted by the filament lamps 1 and is rapidly heated.
If, when heating the wafer by the above described heat treatment device 10 of the light irradiation type, nonuniformity of the temperature distribution in the wafer occurs, a phenomenon arises in the wafer which is called xe2x80x9cslipxe2x80x9d and which means dislocation faults. Here, the danger is that scrap will be produced.
Therefore, when a wafer is being heat treated using a heat treatment device of the light irradiation type, there is a need to control the amount of light irradiation in order to make the temperature distribution of the wafer uniform.
For the light source of the heat treatment device of the light irradiation type, lamps are used which have a filament and which emit IR radiation with high efficiency, as is shown in FIG. 10. When these filament lamps are used over a long time, the material contained in the filament, for example, tungsten, gradually vaporizes, and it is deposited on the wall surface of the inside of the lamp bulb. The locations at which this vapor deposition has occurred are colored black; this is called xe2x80x9cblackening.xe2x80x9d
When blackening occurs in a lamp, the location at which the blackening has occurred no longer transmits the light from the filament. On the surface irradiated with light, directly below the blackened location, the irradiance and the temperature of the surface irradiated with light are reduced. As a result, there are cases in which in the wafer nonuniformity of the temperature distribution arises, and thus, scrap is formed.
During lamp operation, the blackened location more easily absorbs heat energy from the filament. In the state in which blackening is there, if lamp operation continues, the temperature rises until a temperature is reached at which the silica glass of the lamp bulb (of the glass vessel of the lamp, which is hereinafter called xe2x80x9cbulbxe2x80x9d or xe2x80x9cbulb glassxe2x80x9d) softens, by which the bulb is deformed and breaks. Therefore, there is a need for premature replacement of the lamp in which blackening has occurred with a new lamp.
Even in the above described discharge lamp which is used for semiconductor lithography, for curing, drying of ink and adhesive, and for similar purposes, the irradiance on the surface which has been irradiated with light likewise drops when blackening occurs. There are cases in which scrap is produced.
Conventionally, blackening of a lamp is visually determined. That is, in a regular examination, irradiation is stopped, the photoheating chamber and the lamp housing are opened, the state of the lamps in the light source part is visually inspected, and in the presence of blackening, the affected lamps are replaced.
In the above described heat treatment device of the light irradiation type, the lamps are located in a photoheating chamber or in a lamp housing and cannot be examined from the outside. When blackening occurs between two regular inspections in the lamps, therefore, it cannot be determined.
Therefore, there are cases in which blackening of the lamps reduces the irradiance and produces scrap, as was described above, or in which the lamps are heated and therefore damaged.
To eliminate the above described defects, there is a demand for determining the blackening of a lamp in real time or in a state in which the heat treatment device of the light irradiation type is in operation. However, conventionally, there has been no process for determining the blackening of a lamp in real time or during operation.
The invention was devised to eliminate the above described defects. Therefore, a first object of the invention is to devise a process for determining blackening of a lamp without visual inspection in real time or during operation.
A second object of the invention is to devise a process for determining blackening of a lamp in which the blackening of the lamp bulb can be determined regardless of the temperature of the lamp bulb in real time or during operation.
A solid emits spectral radiant energy which corresponds to the respective temperature and which is characteristic for the respective solid according to the principle of solid state emission. This spectral radiant energy emitted by the lamp bulb at the time at which the lamp is not blackened differs from the spectral radiation energy at the time at which the lamp is blackened. Thus, the blackening of a lamp can be determined without visual inspection by determining the change of the spectral radiant energy emitted by the lamp bulb.
The spectral radiant energy also changes with the temperature of a body. In a lamp in which the input power supplied to the lamp and the temperature of the lamp bulb change, there are, therefore, also cases in which, when a change of the radiant energy emitted by the bulb occurs at a single defined wavelength, it cannot be distinguished whether this change was caused by the blackening or by the change of the temperature of the lamp bulb.
In one such case, the radiant energy emitted by the lamp bulb at two different wavelengths (in two different wavelength ranges) is measured and the ratio to one another is determined. This ratio is compared to the value in the case in which no blackening has occurred in the lamp. When the amount of change is greater than or equal to a stipulated value, this means that blackening has occurred in the lamp. In this way, the blackening of a lamp can be determined without visual inspection, even if the temperature of the lamp bulb changes.
In the case of a filament lamp, during lamp operation, the emission part emits an enormous amount of spectral radiant energy. Therefore, there are cases in which the spectral radiant energy emitted by the bulb compared to the energy emitted by the emission part drops into the background and can be perceived only as a background noise level. When, after turning off the lamp and before the bulb cools, the spectral radiant energy is measured, the blackening of a lamp can be determined without the spectral radiant energy emitted by the emission part exerting an effect.
In a discharge lamp there are, furthermore, cases in which the spectral radiant energy distribution in the emission part exhibits peaks. In this case, the blackening of a lamp can be determined without the influence of the spectral radiant energy emitted by the emission part, when the wavelength range in which the spectral radiant energy emitted by the bulb is measured, while avoiding the wavelengths emitted by the lamp emission part with maximum intensity, is chosen such that in this measurement wavelength range the spectral radiant energy emitted by the emission part with respect to the spectral radiant energy emitted by the bulb can be called background noise level and does not disrupt measurement of the energy emitted by the lamp bulb.
The objects are achieved as follows in accordance with the invention:
(1) The radiant energy emitted by the lamp bulb is measured at a stipulated wavelength (in a stipulated wavelength range). This measured value is compared to the measured value at the start of lamp use. When the amount of increase is greater than or equal to a predetermined value, it is assumed that the blackening has occurred in the lamp.
(2) The radiant energy emitted by the lamp bulb is measured at two different wavelengths (in two different wavelength ranges) and the ratio to one another is determined. This ratio is compared to the value in the case in which no blackening has occurred in the lamp. When the amount of change is greater than or equal to a predetermined value, this means that blackening has occurred in the lamp.
(3) In (1) and (2), the radiant energy emitted by the lamp bulb is measured after the lamp is turned off and before the lamp cools.
(4) In (1) and (2), wavelengths are chosen in a region in which the radiant energy emitted by the lamp emission part as compared to the radiant energy emitted by the bulb is somewhat lower. Thus, essentially the radiant energy emitted by the lamp bulb is measured.
In the following, the invention is specifically described using several embodiments which are shown in the drawings.